1. Technical Field
The present disclosure relates generally to a method of compensating for a current sensor offset of an inverter. More particularly, the present disclosure relates to a method and system of compensating for a current sensor offset of an inverter, which are capable of compensating for a current sensor offset due to a temperature change occurring in vehicle driving as well as in vehicle starting.
2. Description of the Related Art
As is well-known to those skilled in the art, a motor for driving an eco-friendly vehicle (e.g., hybrid vehicle or electric vehicle) can output a mechanical torque by a three-phase current having a phase difference of 120° generated by ON-OFF controls of six switches that configure an inverter. The three-phase current is an important factor for determining the torque of the motor and an important role of the inverter is to control the three-phase current.
The inverter requires information such as a direct current (DC) link voltage, a rotor position, or a three-phase current, etc., in order to control the three-phase current. A three-phase current sensor for obtaining the three-phase current among them is an essential component of the inverter.
Typically, most three-phase current sensors physically include an offset voltage (i.e., a voltage detected when a current is 0 A), and the offset voltage of the current sensor becomes a factor causing ripples to an output torque of a motor at the time of three-phase current control and becomes an element for hindering drivability. Accordingly, in order to address such a limitation, the offset voltage of the current sensor is typically compensated with a software-based method.
In addition, the three-phase current sensor has a property that the offset voltage varies at the time of temperature change. For example, when a vehicle travels for a certain time, since the temperature of the three-phase current sensor rises, it is necessary to continuously monitor an offset of the current sensor and compensate for the offset in view of an internal structure of the inverter.
For an existing current sensor offset compensating scheme, the current sensor offset compensation is performed, after it is determined whether a value is a normal offset wherein the value is obtained by passing a filter using a sensed output voltage of the current sensor in a state where a pulse-width modulation (PWM) control of an inverter switch becomes OFF at the time of turning-on a vehicle ignition (i.e., before a start of current control of the inverter).
In other words, since the current sensor offset is conventionally measured once and compensated at the time of ignition ON, a current sensor offset, which is varied by an increase in surrounding temperature due to continuous driving after the compensation, is not considered. Accordingly, a torque error may also occur in a torque output from a motor by the current sensor offset.
The torque error component appears in a sinusoidal wave type having the same frequency as a synchronous rotational frequency of a motor and the torque error appears as motor speed ripples in view of the vehicle, causing an inconvenience for the driver.
The topics described above are only intended to increase the understanding of the background of the present disclosure, and should not be recognized as being related art which is already known to those skilled in the art.